1. Technical Field
The present invention relates to a self-lubricating sliding bearing and, more in particular, relates to a self-lubricating liner composition used on a sliding surface of the self-lubricating sliding bearing.
2. Background Art
Among bearings for supporting a shaft of rotary motion, a sliding bearing in which the shaft is held by a cylindrical sliding surface has been widely used conventionally and, in particular, a self-lubricating sliding bearing in which a lubricating oil or the like is not necessary on the lubricating surface, has been used for applications requiring low friction coefficient, high durability, high load capacity, high heat resistance, high oil resistance and the like, such as aircraft application.
For example, a spherical bearing B5 for use in high load condition, consisting of an outer ring member 13 having a concave first sliding surface and an inner ring member 32 having a convex second sliding surface which is slidable with the first sliding surface, as shown in a sectional view in FIG. 5, is well known (See patent document 1).
In this spherical bearing, one member is made of titanium alloy, and it has a sliding surface treated with titanium nitride applied by a physical vapor deposition method (PVD). The other sliding surface is provided with a self-lubricating liner 23. The self-lubricating liner 23 is composed of a fabric consisting of weaved fibers of PTFE (Polytetrafluoroethylene) and polyaramid. The fabric is saturated with phenol resin. A self-lubricating sleeve bearing in which a similar fabric type self-lubricating liner is bonded on the inner sliding surface has been widely known as a conventional technique.
In addition, a self-lubricating coating consisting of a thermosetting acrylic composition containing 20% by weight or more of dipentaerythritolpentaacrylate and 10% by weight or more of solid lubricating agent such as polytetrafluoroethylene, is disclosed (See patent document 2).
The patent document 2 discloses that 20% by weight or more of triethyleneglycol dimethacrylate and 1% by weight or less of aramid pulp can be added to the self-lubricating coating. Furthermore, a sleeve bearing B6 in which the self-lubricating coating is arranged on the inner sliding surface of the outer ring 14 as the liner 24 shown in FIG. 6 is disclosed.
Furthermore, a sliding bearing for rotatably supporting a rotary shaft of an impeller of a cooling water circulating pump arranged with a fuel cell, in which the constitutional material of the sliding bearing is a synthetic resin such as polyetherketone-based resin free of metallic ion, is disclosed (See patent document 3).
In the patent document 3, polyetheretherketone (PEEK) is mentioned as the synthetic resin not containing metallic ion. To improve the mechanical strength and frictional wearing property of such polyetherketone-based resin, it is desirable to add a fibrous filler such as carbon fiber or aramid fiber and a solid lubricating agent such as fluorine resin or graphite. The fillers may be added at 3 to 60 parts by weight to 100 parts by weight of polyetherketone-based resin. The desirable addition amount of the carbon fiber is 5 to 40 parts by weight to 100 parts by weight of polyetherketone-based resin, and more desirably 10 to 30 parts by weight. As the solid lubricating agent, fluorine resin powder such as PTFE, PFA or the like, and graphite or the like are disclosed. The addition amount of the solid lubricating agent is 1 to 40 parts by weight, desirably 5 to 30 parts by weight, and more desirably 5 to 20 parts by weight to 100 parts by weight of polyetherketone-based resin. The above-mentioned materials for molding are mixed, plasticized by heating until the temperature range of 400 to 420° C., filled into a mold, solidified, and released, to obtain a sliding bearing of cylindrical plastic body.    Patent document 1: Japanese Unexamined Patent Application Publication No. 2007-255712    Patent document 2: U.S. Pat. No. 6,180,574    Patent document 3: Japanese Unexamined Patent Application Publication No. 2006-9819
Since the sliding bearings disclosed in the patent documents 1 and 2 are used in aircrafts, high load capacity, heat resistance, and oil resistance, in addition to low frictional coefficient, are required. Furthermore, for the airframe manufacturers it is convenient that, during an assembling process of a sliding bearing like a sleeve bearing, the fit-adjustment can be performed by adjusting the size of sliding surface diameter of the sleeve bearing by grinding or cutting, instead of performing size adjustment of the shaft diameter.
However, since the fabric type self-lubricating liner disclosed in patent document 1 contains weaved fibers saturated with resin, its diameter size cannot be adjusted by grinding or cutting process because the fibers may be cut and therefore the weaved liner would be damaged.
In addition, productivity of the self-lubricating coating disclosed in patent document 2 is low since it is based on thermosetting acrylic resin.
Furthermore, the sliding bearing disclosed in patent document 3 does not have sufficient strength to be used in an airframe since the sliding bearing are entirely made of resin. In addition, although a resin material free of metallic ions is suitable as a sliding bearing to rotatably support the rotary shaft of an impeller in a cooling water circulating pump, it is uncertain about the use in aircraft application where high load capacity, heat resistance, oil resistance and the like are required.